MR sensors based on Faraday Law detection may couple to both electric and magnetic field components of Radio Frequency Interference (RFI). This RFI is known to emanate from both natural and man-made sources. Electric coupling can occur when common mode voltages on the sensor structure are generated through capacitive coupling to ambient electric fields (such as RF electric field voltages and gradients due to being in close proximity to human limbs). Magnetic coupling can occur when RFI magnetic fields thread the aperture of the sensor used for detection. These magnetic fields may originate from distant transmitters or close-in sources such as nearby power transmission mains wiring.
In applications, such as medical imaging, electromagnetic shielding (such as an electrically conductive box or a shielded room) is used to prevent extraneous RFI from interfering with the MR signal. However, such techniques are not suitable in many potential applications of MR detection. For example, it is not practical to use electromagnetic shielding for bulk material such as mineral containing material being moved on a conveyor or if the MR detection device needs to be portable.